Recently, for the purpose of giving a lithium secondary battery a higher energy density, alloying materials of Al, Sn, Si, and like elements having a high capacity per volume due to an alloying reaction with lithium are being taken up, instead of a graphite material in practical use, as candidates for a novel negative-electrode active material and much studied.
However, in a negative electrode in which a material capable of alloying with lithium is used as an active material, the active material undergoes large volume changes during lithium storage and release, which presents a problem in that the active material may be finely divided or shed off from a current collector to degrade the current collecting performance in the electrode, resulting in a poor charge-discharge cycle characteristic.
In relation to the above problem, it has been found that if, in order to achieve high current collecting performance in a negative electrode, an active material layer containing an active material made of a silicon-containing material and a polyimide binder is disposed by sintering it in a non-oxidizing atmosphere, the resultant negative electrode will exhibit a good charge-discharge cycle characteristic (see Patent Literature 1 below).
Furthermore, it has also been found that by changing the kind of polyimide serving as a negative electrode binder, the cycle characteristic can be further improved (see Patent Literatures 2 and 3 below). Patent Literature 4 discloses that the use of a polyimide composed of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and either m-phenylenediamine or 4,4′-diaminodiphenylmethane enables the cycle characteristic to be improved (see Patent Literature 4 below).